The plan was announced as Russian President Vladimir Putin warned that his country could stop sending gas next month because of Ukraine’s high gas debts.

Polish Prime Minister Donald Tusk said he and his counterparts from Hungary, Slovakia and the Czech Republic agreed Thursday to work on a “solidarity mechanism” for gas supplies.

They didn’t provide details.

Tusk, who spoke at a security conference in Slovakia, wants all EU states to jointly negotiate the price of gas bought from outside providers. He also wants the EU to spend more money on developing energy networks to enable countries to share gas in case of cutoffs or shortages.